In order to reduce carbon dioxide emissions, an engine is proposed on which is mounted an idle-stop mechanism including an integrated starter/generator (ISG) capable of stopping the engine when the vehicle comes to a stop, and instantly starting the engine when the accelerator pedal is depressed, allowing start of the vehicle.
FIG. 11(b) shows a belt transmission device for an engine on which is mounted an idle-stop mechanism including an ISG capable of both driving engine accessories and starting the engine. This belt transmission device includes a crankshaft pulley P1 mounted to the crankshaft 1, a starter/generator pulley P2 mounted to a rotary shaft of the starter/generator 2 of the ISG, an engine accessory pulley P3 mounted to a rotary shaft of an engine accessory 3 such as a water pump, and a belt 4 trained around the pulleys P1 to P3, and is configured such that while the engine is running in a normal state as shown in FIG. 11(a), the starter/generator 2 and the engine accessory 3 are driven by the crankshaft pulley P1, which is rotating in the direction of the arrow in FIG. 11(a). The starter/generator 2 serves as a generator at this time.
To start the engine, the starter/generator 2 is actuated, as a starter, to rotate the starter/generator pulley P2 in the direction of the arrow in FIG. 11(b), thereby rotating the crankshaft pulley P1.
This belt transmission device further includes a tension pulley 5 provided at a portion 4a of the belt 4 extending between the crankshaft pulley P1 and the starter/generator pulley P2 and rotatably supported by a pivotable pulley arm 6, and a hydraulic auto-tensioner A which applies an adjusting force to the pulley arm 6 so as to bias the pulley arm 6 in the direction in which the pulley arm 6 is pressed against the belt 4, thereby absorbing any change in the tension of the belt 4.
Conventional hydraulic auto-tensioners of this type are disclosed in the below-identified Patent documents 1 and 2. Either of these conventional hydraulic auto-tensioners includes a rod having its bottom end portion slidably inserted in a valve sleeve protruding from the bottom surface of a cylinder so as to define a pressure chamber in the valve sleeve; and return spring mounted between a spring seat provided at the top end portion of the rod and the bottom surface of the cylinder, and biasing the rod and the valve in the direction in which the rod protrudes from the valve sleeve.
Further, a sealed reservoir chamber is defined between the inner periphery of the cylinder and the outer periphery of the valve sleeve such that the lower portion of the reservoir chamber communicates with the lower portion of the pressure chamber through oil passages formed in the bottom surface portion of the cylinder; and a check valve is mounted in the bottom end portion of the valve sleeve such that when a push-in force is applied to the rod, and the pressure in the pressure chamber exceeds the pressure in the reservoir chamber, the check valve is closed, thereby blocking communication between the oil passages and the pressure chamber.
Each of these conventional hydraulic auto-tensioners further includes a coupling piece provided on the top surface of the spring seat and pivotally coupled to the engine block shown in FIG. 11(a), and a coupling piece provided on the bottom surface of the cylinder and coupled to the pulley arm 6 shown in FIG. 11(a). In this arrangement, when a push-in force is applied from the belt to the rod through the tension pulley 5 and the pulley arm 6, the check valve is closed, so that oil sealed in the pressure chamber flows into a leakage gap defined between the sliding surfaces of the valve sleeve and the rod, thereby generating a hydraulic damper force in the pressure chamber due to the viscous resistance of the oil flowing into the leakage gap, to damp the push-in force.